In this chapter, the authors present a quite comprehensive theoretical analysis of the phenomenon of strategic voting in the context of different institutional settings, namely in different types of electoral systems – majoritarian, PR and mixed. The incentives present those different institutional settings are discussed. Moreover, the magnitude of this psycho-political phenomenon, draw upon the results of the most relevant statistical works on strategic voting, is examined in detail. The chapter continues with the presentation of the most interesting results uncovered by the empirical analysis of strategic voting in the Portuguese 2005 legislative elections, conducted and published by Bourdain (2007). With this analysis, which used survey data collected by the Portuguese Electoral Behaviour Project right after the elections, it was possible to identify a substantial share of strategic voters (around 6 per cent) and assess the relative impact of demographic, attitudinal and contextual variables on the decision of voting strategically vs. sincerely.